This invention pertains to the art of refrigerant suction accumulators, and especially to a particular construction thereof which is eminently suited for use in a transport refrigeration system unit. For that reason, the accumulator of the invention will be described in such an environment, although it is considered that its use is not limited thereto.
As is well known to those versed in this art, a suction accumulator used in a vapor-compression refrigeration system is interposed between the refrigerant evaporator and refrigerant compressor and has a main purpose of preventing undue quantities of liquid refrigerant from returning to the compressor, while permitting the flow of vaporous refrigerant from the accumulator to the compressor. The typical general construction of a suction accumulator as currently used with transport refrigerations may be generally as shown in U.S. Pat. NO. 3,420,071. As there shown, a return tube from the evaporator delivers refrigerant to the accumulator casing interior upper portion in vapor form and, depending upon conditions, to some degree in liquid form. The liquid refrigerant is intended to drop to the bottom sump portion of the casing, while some vaporous refrigerant is admitted into one end of a U-shaped tube in the upper portion of the casing and flows therethrough to an outlet in the top of the casing and back to the compresor. The U-shaped tube has an oil pickup port in its bight portion which permits the introduction of oil in the liquid refrigerant into the U-shaped tube for return to the compressor. As typically used in a transport refrigeration system environment, the accumulator has a cap or other structure at the bottom into which warm water from the internal combustion engine is circulated to boil off liquid refrigerant if it is present in the sump.
As used in a transport refrigeration system, under certain operating conditions such as a changeover from a cooling mode to a heating, or defrost, mode, and in particular with the evaporator operating at a low temperature and a low ambient existing, a large amount of liquid is dumped into the accumulator. Sometimes this liquid cannot be boiled off fast enough by the heat from the engine water and starts filling up the lower part of the U-tube, thus choking off the cross sectional flow area for the vapor which is supposed to return through the tube to the compressor. This results in high vapor velocities, and hence more liquid is entrained in the vapor to the compressor. Also, as the vapor is boiled off, it causes violent agitation of the liquid in the sump, causing a foamy liquid-vapor mixture. The level of this foam can rise high enough to enter the U-tube directly at the top, thus compounding the liquid carryover to the compressor. Depending upon the conditions, the amount of liquid returning to the compressor is sometimes enough to cause liquid slugging and damage to the compressor parts, and even destruction of the compressor.
The aim of this invention is to provide a suction accumulator construction intended to significantly alleviate the problem of return of liquid refrigerant to the compressor under conditions such as detailed above, as well as under other conditions.